1. Field of Invention
The present invention relates generally to surgical instruments, and more specifically to an apparatus for dissipating electric charge on surgical instruments.
2. Art
The use of robotic surgery, for example the use of da Vinci® telerobotic surgical systems, commercialized by Intuitive Surgical, Inc., Sunnyvale, Calif., is increasing. Robotic surgery allows complex surgical procedures to be executed with minimally invasive techniques. A smaller incision heals faster, is less painful, is less prone to infections, and leaves less noticeable scarring. Teleoperated surgical instruments under endoscopic view often allow a surgeon to carry out actions that are difficult to do with manual instruments. For these and other reasons, patients, surgeons, and hospital personnel are becoming inclined towards robotic surgery over traditional manual procedures (open or minimally invasive).
Robotic surgery instruments include items such as cannulas, graspers, forceps, scissors, retractors, stabilizers, and other instruments that may or may not be made of metal or other electrically conductive materials. Conductive materials may pose a hazard in a surgical environment because they may become electrically charged. When these materials suddenly discharge, the discharge may cause burns or other injuries to the patient, the surgeon, or other personnel as the charge seeks a path to a lower electric potential. Since the discharge arc may be out of the surgeon's field of view, the surgeon may not realize that a patient burn has occurred. And, since the instruments are long, even if a discharge is sensed, it may be difficult to identify the burn location. In addition, such a sudden discharge may damage the instrument itself if the instrument includes electrical components.
Typically, the energy stored in a surgical instrument from capacitive coupling during robotic surgery is transferred to the patient in two ways. First, the stored charge can be drained by keeping the instrument in direct, physical contact with the patient's body. This constant contact conducts electric charge from the instrument to the patient's tissues, which prevents arcing by establishing an equal electric potential on the patient and the instrument. For example, charge that is induced on an instrument cannula that is placed through the patient's body wall will drain to the patient because of the cannula's direct contact with the patient. Second, the stored electric charge may be drained via capacitive coupling to a second instrument that is in direct, physical contact with the patient. As described above, the contact between the second instrument and the patient then conducts the transferred charge to the patient. For example, unwanted charge may build up on certain portions of a monopolar electrocautery instrument, such as on a metal flexible wrist mechanism that supports the energized end effector. Without a conductive path or effective insulation, this charge may arc from the instrument to the patient and cause injury. But this unwanted charge can be safely transferred via capacitive coupling to the cannula though which the electrocautery instrument extends. The transferred charge is then conducted from the cannula to the patient via direct contact.
To conduct the unwanted charge away from the patient, one or more patient return electrodes, such as those associated with an electrocautery instrument, are placed in contact with the patient. The patient return electrode completes a circuit that safely removes the electric charge from the patient, so that arcing does not occur at some other location on the body.
In certain new robotic surgery procedures, however, an instrument that is subject to capacitive coupling will not come into direct contact with the patient's tissues. Therefore, electric charge buildup on the instrument from capacitive coupling occurs because there is no path to drain the built up charge. In transoral robotic surgery (TORS), for example, an instrument cannula is inserted into oral cavity in order to guide and support a telerobotically controlled surgical instrument, but often the cannula does not contact the patient. Therefore, when an electrosurgical instrument (e.g., a monopolar electrocautery instrument) is inserted through a cannula during a TORS procedure, capacitive coupling between the instrument and its cannula may cause electric charge buildup on the cannula. Since the instrument cannula with the charge buildup is often in close proximity to, although not in contact with, the patient's tissues, sufficiently high charge buildup may cause a dangerous electrical arc between the instrument cannula and the patient. Likewise, a person who inadvertently comes near or touches the charged instrument cannula may be similarly injured, or electrical components that come near or touch the charged instrument cannula may be damaged. Similarly, since there is no suitable conductive path from the cannula, unwanted charge that builds up on a portion of the instrument that extends through the cannula (e.g., on one or more electrocautery instrument components) cannot be drained via capacitive coupling to the cannula, because once charged the cannula itself does not offer a relatively lower electric potential.
Since electrical charge buildup is not being continuously dissipated through the patient's body, the charge will remain concentrated on one or more instruments. This concentrated charge buildup creates a hazardous condition, as described above. Consequently, there is a need in the art to dissipate energy from instruments, and specifically an instrument cannula, that do not contact the patient.
The cantilever aspect of a supporting cannula that does not contact the patient presents another potential problem. When an instrument extends through a cannula, heavy side loading on the instrument's distal end pushes the instrument laterally against the cannula's distal end. During withdrawal (e.g., during a surgical procedure as the instrument experiences numerous small insertion and withdrawal motions as the slave instrument responds to the surgeon's teleoperation master inputs), the distal end of a cannula may scrape against the instrument shaft. This scraping may, in some instances, remove a small piece of the shaft, which may then enter a patient.
In order to assure that a cannula can be inserted through a patient's body wall, the distance between the cannula's inner diameter at its distal end and the outer diameter of the cannula obturator used to pierce the body wall needs to be minimized. Otherwise, cannula insertion through the body wall is difficult. But when the obturator is removed and replaced with an instrument, the cannula's distal end configuration that is needed for proper insertion through the body wall may lead to instrument shaft scraping under high instrument side loads. Therefore, there is a need to prevent scraping contact between a cannula's distal end and the instrument shaft.